Non-syndromic CP and CL(P) exemplify complex birth defects with both multigenic and environmental contributions. However, relatively little is known about the developmental or genetic basis for orofacial clefting. This may relate to heterogeneity in the combinations of genes that predispose to CP and CL(P), and to constraints imposed by human genetic variation. We suggest that the mouse offers certain advantages for furthering our genetic and molecular understanding of CP and CL(P). Specifically, the large battery of available mouse orofacial clefting mutants provides a unique opportunity to develop a systematic, mechanism-based classification for genes whose function is required for palatogenesis. We posit that mouse clefting mutants can be grouped into specific developmental classes based on the step at which the respective genes act. Moreover, we propose that within each class of mutants, genes that are co-expressed, or that - based on existing functional annotation - can be logically considered to act within a specific pathway, should have a high likelihood of interacting genetically when the respective mutant alleles are compounded. Conversely, genes that reside in different classes should not. In this way, we hope to begin to model the complex inheritance of CP and CL(P). In Aim 1, we will clone the genes for four new recessive mouse clefting mutants generated in our ENU mutagenesis screen. Three mutants, cpo1, ctcp and Ic express a cleft secondary palate, and we have already cloned cpo1, revealing a novel Zn-finger gene. A fourth mutant, clf3, expresses isolated cleft lip. In Aim 2, we will analyze the mutant phenotypes in comparison with existing mouse clefting mutants to determine the specific developmental step at which each gene acts. Lastly, in Aim 3, we will test specific hypotheses about the relationship between the respective genes and their products. This will involve carefully selected developmental and molecular experiments, and the generation of genetic compound heterozygotes to test whether combinations of the recessive loci identified model the complex inheritance of CP or CL(P). In sum, these experiments should identify new genes involved in orofacial clefting, advance our understanding of the developmental mechanisms involved, integrate the genes into developmental and molecular pathways, and reveal how these loci interact genetically to contribute to orofacial clefting. [unreadable] [unreadable]